JP-A-4-234386 discloses carbostyril derivatives represented by the general formula (A), ##STR2## (wherein R.sup.A is a hydrogen atom or a lower alkyl group; R.sup.B is a hydrogen atom, a lower alkyl group or a lower alkoxy group; and R.sup.C is a lower alkyl group respectively) which can be used as intermediates for preparing other carbostyril derivatives used for treating cardiovascular diseases.
Additionally, WO 93/22317 discloses carbostyril derivatives represented by the general formula (B), ##STR3## (wherein R.sup.D and R.sup.E are each the same or different from each other and are hydrogen atoms, lower alkyl groups or lower alkoxy groups; and the carbon--carbon bond between 3- and 4-positions in the carbostyril skeleton is a single bond or double bond) which can be used as intermediates for preparing quinoline derivatives used for remedy for cardiac diseases.
However, these prior art references disclose only that the above-mentioned carbostyril derivatives can be used as intermediates for preparing blocking agents of adrenaline .beta.-receptor or antiarrhythmic drugs. Thus, above-mentioned prior art references do not disclose at all that these carbostyril derivatives per se possess whatever pharmacological activities.
Furthermore, WO 97/44037 and WO 97/44321 disclose quinoline compounds as antagonists of gonadotropin-releasing hormone, and WO 97/03066 discloses substituted benzolactam compounds as substance P antagonist. In fact that these quinoline compounds and substituted benzolactam compounds involve carbostyril skeleton in their molecular structures. However, these compounds are quite different from the carbostyril derivatives of the present invention in both chemical stractures and usages.